The outcome of an orthopedic procedure is highly dependent on the accuracy of the determination of implant size and placement within the bones or bone parts that are the subject of the procedure. A large number of post-operative and intra-operative complications can result from the use of an incorrectly sized or poorly placed implant, including complications from implant breakage or loss of fixation subsequent to the procedure.
In attempting to achieve accurate implant selection and positioning, guiding devices have been developed for the preparation of bone to receive implants as well as to receive implants in view of specific indications or conditions. Many of these devices have been developed or adapted for use with relatively large joints or bones. However, these devices often do not assist in the placement of implants, in particular medical bone screws, through multiple small bones or bone fragments of limited size, as often required in some surgeries of the foot or hand. Lisfranc joint arthrodesis, calcaneocuboid arthrodesis or scaphoid fracture fixation are a few examples of hand and foot procedures in which there is a lack of adequate instrumentation for the correct sizing and placement of implants, especially minimally invasive or non-invasive instrumentation.
Jones fractures, i.e., proximal fifth metatarsal fractures, are another example of indications where there is a lack of such instrumentation. The most common surgical treatment of these fractures involves a bone screw inserted through the medullary cavity of the fractured bone. An implanted screw should be positioned in the center of the intramedullary cavity to achieve optimal fixation and to avoid potential bone damage. An implanted screw also should have a width large enough to have endosteal purchase but small enough to avoid bone splitting or cracks. The screw further should have sufficient length to have satisfactory purchase and adequate fracture-bridging but should be short enough to avoid opening the fracture gap due to straightening the bone during screw insertion.
Some sizing instruments, such as length and depth gauges have been included in orthopedic instrument kits for use with the placement of medical bone screws. Such instruments aid in determining the appropriate screw length but often not the appropriate cross-section, width, or diameter best matching a patient's anatomy and indication. Screw taps have been used to determine both the length and diameter of a bone screw. However, taps are compulsorily implant-specific as they should have the same thread characteristics as the corresponding screw implant. Moreover, being invasive instruments, taps having an oversized diameter may cause a procedure to be halted or detrimentally impact the performance of an inserted implant and may even cause irreversible bone damage.
Therefore, there is a need for an instrument that aids in properly sizing and placing an implant through multiple small bones or bone fragments of limited size in a non-invasive manner.